Aluminum has been commonly used as a metal wiring material because it is easily deposited on wafers, etched with a solution that does not attack films under aluminum, and low-priced. However, as the semiconductor device is becoming highly integrated, the number of metal wirings increases and a pitch of metal wirings decreases. The reduction in the pitch of the metal wiring leads to an increase in a wiring resistance and causes an RC delay due to an increase in parasitic capacitance formed between adjacent wirings, thereby degrading a speed of the semiconductor device.
Thus, in line with the high integration of the semiconductor device, a method for lowering the wiring resistance has been studied, and as a solution, copper (Cu) having a low specific resistance and good reliability compared with aluminum (Al) has been adopted as a material of the metal wiring.
However, a copper wiring is disadvantageous in that it is not easily patterned through plasma etching unlike the aluminum wiring. Thus, in order to form the copper wiring, a dual damascene method is used, in which an insulation film is first deposited and etched, and then, copper is deposited and filled therein.
However, the dual damascene method can be hardly applied for the aluminum wiring process. Thus, in order to lower the wiring resistance, the thickness or the width of the aluminum wiring needs to be increased, and even in this case, actually, there is a limitation in lowering of the wiring resistance.